Testing an electronic circuit for possible defects can result in a significant amount of test data (for example, test responses), particularly if the circuit is large and/or complicated. Test responses stored by scan chains in a circuit can be compressed, for example, to allow for the responses to be analyzed using fewer test resources (for example, test pins), possibly by automated testing equipment (ATE) external to the circuit. Test response compactors exist, but the compaction ratio of these devices is often limited to the ratio of the number of scan chains to the number of compactor outputs. Accordingly, there is a need for compaction schemes providing potentially higher compaction ratios.